Nuclear magnetic resonance spectroscopy, or NMR, is a powerful and commonly used method for analysis of the chemical structure of molecules. NMR provides spectral information as a function of the electronic environment of the molecule and is nondestructive to the sample. In addition, reaction rates, coupling constants, bond-lengths, and two- and three-dimensional structure can be obtained with this technique.
Systems for biochemical, chemical, and molecular analysis can be miniaturized as capillary-based systems or substrate-based, i.e., micro-scale, systems with multifunctional capabilities including, for example, chemical, optical, fluidic, electronic, acoustic, and/or mechanical functionality. Miniaturization of these systems offers several advantages, including increased complexity, functionality, and efficiency. Devices can be fabricated from diverse materials including, for example, plastics, polymers, metals, silicon, ceramics, paper, and composites of these and other materials. Mesoscale sample preparation devices for providing microscale test samples are described in U.S. Pat. No. 5,928,880 to Wilding et al. Devices for analyzing a fluid sample, comprising a solid substrate microfabricated to define at least one sample inlet port and a mesoscale flow channel extending from the inlet port within the substrate for transport of a fluid sample are described in U.S. Pat. No. 5,304,487. Currently known miniaturized fluid-handling and detection devices have not met all of the needs of industry.
NMR is one of the most information-rich forms of biochemical, chemical, and molecular detection and analysis, and remains highly utilized in a wide range of health-related industries, including pharmaceutical research and drug discovery. One of the fundamental limitations of NMR for these and other applications involves sample throughput. When compared to other forms of detection (e.g., mass spectrometry), the amount of sample required by NMR is generally orders of magnitude greater, and correspondingly the mass limits of detection are generally orders of magnitude poorer. Conventional NMR spectrometers typically use relatively large RF coils (mm to cm size) and samples in the ml volume range, and significant performance advantages are achieved using NMR microcoils when examining very small samples. Prior to such development of microcoil NMR and NMR flowprobes, NMR remained a test tube-based analytical technique requiring milliliters of sample and often requiring data acquisition times ranging from 10 min. to several hours for informative spectra with sufficient signal to noise ratio (“S/N”). NMR microcoils are known to those skilled in the art and are shown, for example, in U.S. Pat. No. 5,654,636 to Sweedler et al., and in U.S. Pat. No. 5,684,401 to Peck et al., and in U.S. Pat. No. 6,097,188 to Sweedler et al., all three of which patents are incorporated herein by reference in their entireties for all purposes. A solenoid microcoil detection cell formed from a fused silica capillary wrapped with copper wire has been used for static measurements of sucrose, arginine and other simple compounds. Wu et al. (1994a), J. Am. Chem. Soc. 116:7929–7930; Olson et al. (1995), Science 270:1967–1970, Peck (1995) J. Magn. Reson. 108(B) 114–124. Coil diameter has been further reduced by the use of conventional micro-electronic techniques in which planar gold or aluminum R.F. coils having a diameter ranging from 10–200 .mu.m were etched in silicon dioxide using standard photolithography. Peck 1994 IEEE Trans Biomed Eng 41(7) 706–709, Stocker 1997 IEEE Trans Biomed Eng 44(11) 1122–1127, Magin 1997 IEEE Spectrum 34 51–61.
Miniature total analysis systems (μ-TAS) are discussed in Integrating Microfluidic Systems And NMR Spectroscopy—Preliminary Results, Trumbull et al, Solid-State Sensor and Actuator Workshop, pp. 101–05 (1998), Magin 1997 IEEE Spectrum 34 51–61, and Trumbull 2000 47(1) 1–6. The Trumbull et al. device integrated multiple chemical processing steps and the means of analyzing their results on the same miniaturized system. Specifically, Trumbull et al. coupled chip-based capillary electrophoresis (CE) with nuclear magnetic resonance spectroscopy (NMR) in a μ-TAS system.
Capillary-based liquid chromatography and microcoil NMR have compatible flow rates and sample volume requirements. Thus, for example, the combination of the Waters CapLC™ available from Waters Corporation (Milford, Mass., USA) and the MRM CapNMR™ flow probe available from MRM Corporation (Savoy, Ill.), a division of Protasis Corporation (Marlborough, Mass., USA) provides excellent separation capability in addition to UV-VIS and NMR detection for mass-limited samples. The Waters CapLC™ has published flow rates from 0.02 μL/minute to 40 μL/minute. A typical CapLC on-column flow rate is 5 μL/min, the autosampler-injected analyte volume is 0.1 μL or more, and accurate flow rates are achieved through capillary of typically 50 μm inner diameter. The NMR flow cell has a typical total volume of 5 μL with a microcoil observe volume of 1 μL. A typical injected sample amount for CapLC-μNMR analysis is a few μg (nmol) or less.
Capillary scale systems also are shown in U.S. Pat. No. 6,194,900, the entire disclosure of which is incorporated herein by reference for all purposes. In such systems, a capillary-based analyte extraction chamber is connected to an NMR flow site, such as by being positioned as an operation site along a capillary channel extending to the NMR flow cell.
Small volume flow probes are shown, for example, by Haner et al. in Small Volume Flow Probe for Automated Direct-Injection NMR Analysis: Design and Performance, J. Magn. Reson., 143, 69–78 (2000). Specifically, Haner et al show a tubeless NMR probe employing an enlarged sample chamber or flowcell. Microcoil-based micro-NMR spectroscopy is disclosed in U.S. Pat. Nos. 5,654,636, 5,684,401, and 6,097,188, the entire disclosures of all of which are incorporated herein by reference for all purposes. Sample amounts can now range as small as several hundred microliters for conventional flowprobes to smaller than 1 uL for microcoil-based capillary-scale flowprobes. Acquisition times typically range from minutes to hours. The most expensive and technologically limiting component of the NMR system is the superconducting magnet. Although significant financial and technical investment has been made in the development of elaborate mechanical (robotic-controlled) sample changers and, more recently, automated flow injection systems for repetitive and continuous sample throughput, the magnet remains today a dedicated component in which only sequential, one-at-a-time analysis of samples is carried out.
NMR is one of the few analytical methods in which parallel data acquisition has not been applied to increase sample processing functionality, such as the number of samples that can be tested in a given time. At least some of the difficulties in accomplishing this objective are intrinsically related to the hardware involved in NMR data acquisition.
Recent academic results have shown that some of the limitations of NMR processing can be overcome by the use of multiple microcoil detectors in a wide-bore magnet. Proposed designs for incorporating multiple solonoidal microcoils into a single probe head are presented by Li et al. in Multiple Solenoidal Microcoil Probes for High-Sensitivity, High-Throughput Nuclear Magnetic Resonance Spectroscopy, Anal. Chem., 71, 4815–4820, 1999. A dual channel probe for simultaneous acquisition of NMR data from multiple samples is shown by Fisher et al. in NMR Probe for the Simultaneous Acquisition of Multiple Samples, J. Magn. Reson., 138, 160–163 (1999). Such devices, however, have not been commercially implemented and have not been shown to be commercially viable. In addition, higher numbers of multiple microcoil detectors are needed that are compatible also with narrow bore magnets, since narrow bore magnets are predominant in industrial settings. There is also both need for and benefit of microcoil NMR probes having enhanced sample processing functionality.
Accordingly, it is an object of the present invention to provide multi-microcoil NMR microfluidic devices having enhanced sample processing functionality. It is a particular object of the invention to provide improved microcoil NMR detectors for capillary-scale, high resolution NMR spectroscopy probes that can be adapted in accordance with certain preferred embodiments for use in large or small bore magnets and that are capable of enhanced sample processing functionality. Given the benefit of this disclosure, additional objects and features of the invention, or of certain preferred embodiments of the invention, will be apparent to those skilled in the art, that is, those skilled in this area of technology.